Object synchronization in shared object space

ABSTRACT

A system for synchronizing shared objects among multiple applications each running inside its own virtual machine.

BACKGROUND OF THE INVENTION

The present invention relates to a system for synchronizing sharedobjects among multiple applications each running inside its own virtualmachine.

Computer hardware and storage media can only create, store, and processbinary information, i.e. information written using only two digits, “0”and “1”. A compact disc, for example, has a surface subdivided into tinysections that are either pitted (1) or not pitted (0) such that a lasercan detect the presence or absence of pits. Similarly, microprocessorshave inputs and outputs to which a reference voltage either is (1) or isnot (0) present. (Microprocessors repeatedly measure the voltage at eachinput and output at regular intervals, or cycles—hence the speed of aprocessor is expressed in cycles per second, or “Hertz.”) Accordingly,any computer program, as well as any data used in that computer program,must first be expressed in binary code for a computer to run the programor process the data.

Though binary code is conceptually simple, its use to performcomputerized tasks introduces two drawbacks. First, binary code is arelatively inefficient way to express information. As a simple example,the number “100” in decimal notation is expressed as “1100100” in binarycode, and therefore must at a minimum occupy seven “pits” on a compactdisc and/or occupy either a single input of a processor for seven cycles(if entered serially) or seven inputs for one cycle (if entered inparallel). In technical terms, the space that a piece of informationoccupies, or alternatively the number of time cycles a piece ofinformation occupies, is referred to in “bits.” That is to say, thenumber “100” is a 7-bit number because it takes seven digits to expressin binary code. The number “101” is also a 7-bit number, coded as1100101, as is every number between “64” (1000000) and “127” (1111111).

In computer applications, binary code is even more inefficient becausecomputerized information is, by convention, typically expressed inmultiples of 8 bits, e.g. 8-bit, 16-bit, 24-bit, etc. The reason forthis convention is that a computer processing or storage device has nophysical way of distinguishing when one number ends and another numberbegins. Accordingly, the convention is to write a program that specifiesthe bit-rate, i.e. the number of bits that each piece of data processedin the program will occupy. If a program is written in 8-bit code, forexample, every piece of data occupies eight bits, e.g. the number 0 iscoded as 00000000, the number 1 is coded as 00000001, and the number 255is coded as 11111111. In 8-bit code, therefore, every piece of data hasa value between 0 and 255 and every piece of data occupies 8 bits evenif it could theoretically be represented by a single bit. If a programrequires that any piece of data take on a value greater than 255, thebit-rate for the program must be increased incrementally to 16-bit,24-bit, etc. as appropriate.

A computer program operating in binary code may therefore use atremendous amount of storage space and processor cycles, particularlywhen graphics are involved. For example, a photographic quality image isoften coded at 24-bits for every pixel. If the image resolution is 2million pixels, as is common with today's digital cameras, each imagewould occupy 48 million bits, or 4 Megabytes, where a byte is defined as8 bits per byte (due to the convention of expressing binary code inmultiples of 8 bits). Manipulating that image would similarly require 48million cycles of processor time for each manipulation. The amount ofstorage space and processing time increases exponentially whenmanipulating video because the computer system must process and storemany such images every second. In addition, there are many othercomputer applications that are at least as intensive as imageprocessing. Applications of such intensity tend to slow considerably asdata is “bottlenecked” in the computer system.

One way of minimizing the impact of the inefficiency of binary code hasbeen to increase the amount of storage space and processing speed ofcomputers. For example, personal computers sold commercially today offerup to 300 gigabytes (300 billion bytes) of hard drive storage, 4gigabytes (4 billion bytes) of temporary memory storage, and processingspeeds of over 4 gigahertz (4 billion cycles per second). Businesscomputers, such those used in the motion picture industry are evenfaster and include more storage. In other words, as computerapplications have demanded more storage space and processing time, thecomputers have become faster with higher storage capacity. Still, whilethese numbers are impressive, computer systems are not sufficiently fastas to eliminate all bottlenecks, and in fact, as computers become fasterwith more available storage, new applications are developed to takeadvantage of the improved technology so as to provide the need for evenfaster computers, even more storage space, etc.

Another way of minimizing the impact of the inefficiency of binary codeis to write computer programs and applications as efficiently aspossible. Thus there is always an emphasis on writing computer code thatachieves its outcome in as few steps or calculations as possible.Similarly, a computer program should not be written in 24-bit code whenonly 8-bit code is required for the application, and the computerprogram may compress data when appropriate.

A second drawback of using binary code to perform computerized tasks isthat it is impractical to write a computer program in binary code,particularly with complex programs. The first rudimentary computers, forexample, were operated by mechanically toggling electrical switchesbetween on and off states to enter a sequence of binary instructions.Computer programs simply specified the sequence of binary instructionsto enter. This method was feasible so long as the program was no morethan about a hundred instructions long. Beyond that point, programmingdirectly in binary code became too complex, and programs too difficultto correct, or debug. Moreover, because the binary instructions weredependent upon the particular electrical circuitry of the computerprocessor and related hardware, the programmer was required to know indetail the particular architecture of the computer being used by theprogram.

To accommodate computer programs of increasing complexity, as well as tofacilitate the introduction of personal computers into the marketplace,modern operating systems were developed. Early computer operatingsystems, such as Microsoft DOS, essentially acted as an interface with acomputer's hardware so that a user could issue specific commands orinstructions to the computer written in more ordinary language. Theoperating system would recognize the commands, and automatically issuethe instructions to the computer in binary code. For example, inMicrosoft DOS, entering the command “MEM” into the computer would resultin the computer displaying the types and amounts of computer memoryavailable. The person issuing the command did not need to know anythingabout binary code or the manner in which the command being enteredproduced the desired result. The user simply needed to either memorizeor look up a set of commands in an instruction manual.

Further, early operating systems recognized simple programminglanguages, such as BASIC and FORTRAN, written in terms more intuitivethan binary code. In these languages, commands such as WRITE, READ,LOOP, SET and other intuitive terms provided a means to write computerprograms in a manner easily learned and perhaps more importantly, in amanner more easily readable when debugging the program. A simplecomputer program to calculate the area of a circle, for example, mighthave been written in BASIC approximately in this form: 10 PROGRAM 1 20WRITE “This is a program to calculate the area of a circle.” 30 WRITE“Please enter the radius of the circle” 40 READ R 50 SET A = Π*R{circumflex over ( )}2 60 WRITE “The area of the circle is” R 70 END

In this example, after a person typed “RUN PROGRAM 1”, the computerwould execute the command lines in numerical sequence, whereby a personwould be prompted to enter the value for a radius, defined as “R”, afterwhich the computer would square that value, multiply the squared valueby pi and print out the computed area. Writing this same program inbinary code not only would have required much more time and effort onthe part of the programmer, but the programmer also would have had toknow the technical specifications of the computer processor. Obviously,the introduction of operating systems along with intuitive programminglanguages was a boon to both consumers and computer programmers.

A number of such operating systems and programming languages becameprevalent. For example, Apple Macintosh and Microsoft Windows operatingsystems improved (from a consumer's perspective) upon simple text-basedoperating systems such as DOS by allowing user to issue instructions tothe computer using a point-and-click graphical interface displayed on acomputer monitor. Computer applications, such as word processingprograms, computer games, and a host of others took advantage of thisfunctionality to provide products that could be used more intuitivelythrough the graphical interface. Today, a host of operating systems areused, such as many versions of Microsoft Windows 9x, Macintosh OS,Linux, Windows NT, among others.

A wide variety of programming languages also became prevalent. At first,most new programming languages followed the model of the early FORTRANlanguage by structuring the programming language as a series of commandsby which a programmer would issue instructions to a computer in alogical order. The most popular of these language types is a programcalled “C.” The creation of “C” is considered by many to have marked thebeginning of the modern age of computer languages. “C” successfullysynthesized what had seemed to be conflicting attributes of severalexisting programming languages, adding new attributes to form a single,powerful structured language that also happened to be easy to learn.Moreover, it was a programmer's language. Prior to the development of“C”, computer languages were generally designed either as academicexercises by engineers or designed by bureaucratic committees. “C”,however, was developed by programmers, reflecting the way theyapproached the task of programming. As a result, “C” found wide andrapid acceptance in the programming community, attracting many followerswho had near-religious zeal for it.

Once again, however, the increasing complexity of computer programsexposed an underlying flaw of “C” as well as its predecessors. Each ofthese programming languages requires that a program be written as aseries of linear steps or instructions (with an occasional loop orbranch thrown in). In fact, writing such a program is similar toconstructing a geometric proof, and like a proof, once a program such asC or FORTRAN exceeds a certain number of steps (somewhere between 25,000and 100,000 lines of code), the program becomes too complex writeeffectively.

Therefore a new approach to computer programming began to findacceptance in the programming community, commonly referred to asobject-oriented programming. Object-oriented programming approaches aprogramming task in roughly the same way that a person's mind mightapproach that task—by abstracting a solution. Rather than defining aseries of steps, or instructions by which a task could be accomplished,an object-oriented program focuses first on a program's data, definingclasses of data and objects, where an object is a particular instance ofa class. An object-oriented program still contains instructions,referred to as methods, which often are embedded within the classes orobjects themselves. An example of a simple object oriented program thatdisplays the volume of two boxes might look like this: class Box {  double width;   double height;   double depth;   // display volume ofa box   void volume ( ) {    System.out.print (“Volume is ”);   System.out.println (width*height*depth);   } } class BoxDemo {  public static void main (String args[ ] {    Box mybox1 = new Box ( );   Box mybox2 = new Box ( );    // assign values to mybox 1's variables   mybox1.width = 3    mybox1.height = 20    mybox1.depth = 15    //assign values to mybox2's variables    mybox 2.width = 3   mybox2.height = 6    mybox2.depth = 9   // display volume of mybox1  mybox1.volume ( );   // display volume of mybox2   mybox2.volume ( )

In this example program, a box class is first defined having thevariables of width, height, and depth (the term “double” identifies thetype of number that the variable is allowed to be). The box class alsodefines a method to display the volume of an object box of this class bymultiplying width by height by depth. Once this class has been defined,the program defines a second class BoxDemo which includes two objects ofthe initial box class. The class BoxDemo then twice calls the method ofthe first box class for displaying the volume of a box, once to displaythe volume of mybox 1 and once to display the volume of mybox2.

Object oriented programming has quickly gained widespread popularity.One particularly popular object oriented language is called Java, whichis the programming language used in the foregoing example. The reasonJava has become so popular is its versatility in defining classes andobjects, as well as its ability for one class or object to callfunctions in other classes and objects as well as to reuse data in otherobjects simply by referencing the function or the data. In Java,therefore, it is very easy to create multiple variations of a definedclass, to create new variations of an old class, and to reuse a methodpreviously defined by one class in a new class. Parenthetically, anotherobject oriented programming language that has become popular is C++,which expands C to include the functionality of both object orientedprogramming and the instruction oriented programming of C.

Java, like any other programming language relies upon an interface toconvert the program to the required binary instructions. With Java, thisinterface is called a “Virtual Machine” (VM) because the interfacebehaves as if it were a computer unto itself. Every time a Java basedcomputer application is initiated, the application initiates a VM to runthe, application. The Java VM will be described in much greater detaillater in this specification, but several important principles will beintroduced now. First, while the input to a Java VM is always the Javaprogramming language, the output of a Java VM is customized to theparticular platform, or operating system, that hosts the Java VM. Inother words, every Java application must be customized to the hostoperating system so that the VM that it creates is capable of convertingthe Java programming language to the commands unique to the hostoperating system, which in turn issues the appropriate binaryinstructions to the computer.

Second, Java VMs are designed to be independent of one another. If twoJava applications are running on the same computer, each applicationcreates its own VM which is self sufficient, i.e. neither VM needs relyupon the VM of the other application. If one application should close,the other application will not be affected. This often becomesproblematical, however. Recall that even with today's processors andstorage devices, a computer's resources may still be strained byintensive applications. With multiple Java applications runningsimultaneously, each creating its own VM, system resources may bestrained and slowdowns may result. In other words, there is often atrade off between the desired independence of multiple Java applicationsand the speed at which the applications may run.

Third, the creators of the Java VM, Sun Microsystems, emphasizeduniformity of the Java VM with respect to all of the host operatingsystems. Thus, while the “guts” of each VM will of necessity bedifferent across each platform, a user of a Java VM was not intended tobe able to recognize any difference, seeing the same functionalityregardless of the host platform. This, however, became problematical.Many operating systems offer unique features not available to otheroperating systems. Thus a business operating on Windows NT might desireto have a Java VM, and hence the Java application running the VM, takeadvantage of that unique functionality. The same would hold true for auser of a Macintosh or a Linux system, or a Windows 9x system, etc.Therefore, although Sun Microsystems's Java VM is uniform across allplatforms, an industry has blossomed by which Java applications may betruly customized to a host operating system whereby the features of thehost operating system are more fully exploited, and custom tailored tothe particular needs of the business or person running the application.

This diversity among Java VMs tends to hinder the improvement of theJava VM and the programming language because many such improvements aretied to the particular species of Java VM upon which the improvement wasdeveloped. Many businesses may like the particular improvement, butdislike other aspects of the Java VM. In that instance, a business withits own custom or proprietary VM would have the options of buying thenew VM with its perceived advantages and faults, or spend the time andresources to engineer its own VM, which it likes, to include the newimprovement. Exacerbating this problem is that the new improvement maybe proprietary, thus eliminating the second option.

What is desired then, is an improved system for implementingobject-oriented computer applications that both efficiently allocatescomputer hardware resources among multiple computer applications runningsimultaneously on the same computer or network of computers, or amongmultiple threads of a single computer application running on a computeror network of computers, while also preserving the independence ofmultiple, simultaneous applications. What is further desired is such animproved system that is sufficiently flexible so as to be compatible notonly with the diverse range of existing object-oriented computerapplications, but also with object-oriented applications that aredeveloped or modified in the future.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified architectural schematic of an existing VM.

FIG. 2 is an expanded architectural schematic of the VM of FIG. 1showing a memory region interposed between the class loader and theexecution engine.

FIG. 3 is a schematic of the heap shown in FIG. 2.

FIG. 4A is a diagram showing a prior art system for operating multipleVM applications on a host computer.

FIG. 4B is a diagram showing a prior art system for the simultaneousoperation of multiple instances of a VM application on several hostcomputers connected through a network or internet server.

FIG. 5 is a diagram showing a first improved system for operatingmultiple VM applications on a host computer.

FIG. 6 is a diagram showing a first manner in which objects may beshared between applications using the system of FIG. 5

FIG. 7 is a diagram showing a second manner in which objects may beshared between applications using the system of FIG. 5

FIG. 8 is a second improved system for operating multiple VMapplications on a host computer.

FIG. 9 is an improved system for the simultaneous operation of multipleinstances of a VM application on several host computers connectedthrough a network or internet server.

FIGS. 10A and 10B show a system for synchronizing locks on objectsshared in a shared object space.

DETAILED DESCRIPTION

FIGS. 1-4B show a simplified architectural schematic of an existing JavaVM 10, although it should be understood that other types of VMs besidesJava may also have the features shown in FIGS. 1-4B. Referringspecifically to FIG. 1, when a Java application is initiated on a hostcomputer with a host operating system 12, the Java virtual machine (VM)10 loads the application which may include a class loader 16 and anexecution engine 18. Although FIG. 1 indicates a single class loader, inactuality, a Java VM may include multiple class loaders. Thus the classloader 16 may be considered a subsystem that may involve many classloaders. The Java VM 10 has a flexible class loader architecture thatenables a Java application to load classes in custom ways.

Specifically, the class loader 16 may comprise a system class loader andone or more user-defined class loaders. The system class loader is apart of the Java VM implementation and loads classes, including the Javaapplication programming interface (API) class files 20, in some defaultway and usually from the local disk of the host computer. As previouslystated, the particular default manner in which the system class loaderloads classes is specific to the particular VM implementation being usedand may be customized. The term “system class loader” is sometimesreferred to as a “primordial class loader”, a “bootstrap class loader”,or a “default class loader.”

At run time, a Java application may also load application class files 22in custom ways through user-defined class loaders, such as bydownloading class files across a network. While the system class loaderis an intrinsic part of the VM implementation, the user-defined classloaders are not. Instead, user-defined class loaders are written inJava, compiled to class files, loaded into the virtual machine, andinstantiated just like any other object, becoming a part of theexecutable code of a running Java application. User defined classloaders enable a programmer to dynamically extend a Java application atrun time. As the application runs, it can determine what extra classesare needed and load them through one or more user-defined class loaders.Because the user defined class loaders are written in Java, classes canbe loaded in any manner expressible in the Java programming language.

For each class loaded by the virtual machine 10, the virtual machine 10records which class loader loaded the class. When a loaded class refersto another class, the virtual machine 10 requests the referenced classfrom the same class loader that originally loaded the referencing class.For example, if the virtual machine 10 loads the class “Volcano” througha particular class loader, it will attempt to load any classes to whichVolcano referred with the same class loader. In this way, Java'sarchitecture enables a programmer to create multiple “name spaces”inside a single Java application. Each class loader in the executingJava application has its own name space, which is populated by the namesof all the classes it has loaded.

The execution engine 18 executes instructions contained in the methodsof loaded classes in “bytecode”, essentially-Java's machine language.The Java specification describes what is to result from a giveninstruction retrieved from a Java method, but a programmer of a Javaapplication determines the best way of achieving the result usingsoftware, hardware, or a combination of both. The execution engine 18 isan abstraction; Java is a programming language capable of simultaneouslyrunning multiple threads, i.e. distinct paths of execution, hence theexecution of each thread can be considered an “instance” of the abstractexecution engine 18. Thus at any given time, there may be multiple“instances” of the execution engine 18.

The execution engine 18 receives a bytecode stream of instructions in athread and executes the thread one instruction at a time. The executionengine 18 executes the actions requested by each thread, and wheneverintended by the Java application, sends instructions to the operatingsystem in the code that the operating system recognizes. From time totime, the execution engine 18 might encounter an instruction thatrequests a method written in some other language than Java, referred toas a “native method.” On such occasions, the execution engine 18 willattempt to invoke that native method by accessing native methodlibraries 36 through a native method interface 34 (shown in FIG. 2).When the native method returns, the execution engine 18 will continueexecuting the next instruction in the bytecode stream.

When the Java virtual machine 10 runs an application, it needs memory tostore many items, including information it extracts from class files,objects that the program instantiates, parameters to methods, returnvalues, local variables, and intermediate results of computations. TheJava VM 10 organizes the memory it needs to execute a program intoseveral runtime data areas, depicted in FIG. 2. These runtime areas mayinclude a method area 24, a heap 26, one or more Java stacks 28, one ormore program counter (PC) registers 30, and one or more native methodstacks 32. Although the same runtime data areas exist in some form inevery Java VM implementation, the structural details of these areas areleft to the designers of the VM and may therefore vary considerably fromone Java application to another.

Each instance of a Java VM 10 has one method area 24 and one heap 26.These areas are shared by all threads running inside the VM 10. As eachthread comes into existence, it receives its own PC register 30 and Javastack 28. When the VM 10 runs a method contained in a thread, severalthings happen. First, the value of the PC register is used to tell thenext instruction in the method's sequence to execute. Second, thethread's java stack 28 stores the state of each executing Java method ina stack frame, which includes the thread's local variables, theparameters with which it was invoked, its return value if any, andintermediate calculations. When the VM 10 has invoked a method in athread and that method subsequently completes, the VM 10 discards thestack frame for that method from the Java stack 28. The state of nativemethod invocations is stored in the native method stack 32 in a mannerdictated by the designer of the Java VM 10.

Information about loaded data types are parsed from class files as theyare loaded and stored in the method area 24. A data type refers to theformat in which the data is expressed, e.g. an integer, a float, etc. Adata type could also be an address of an op code within a method or areference to an object on the heap 26. The VM 10 uses the typeinformation stored in the method area 24 as it executes the applicationit is running.

For each data type the VM 10 loads, it should store the following kindsof information in the method area: (1) the fully qualified name of thetype; (2) the fully qualified name of the type's superclass; (3) whetheror not the type is a class or an interface; (4) the type's modifiers;(5) an ordered list of the fully qualified names of any directsuperinterfaces; (6) the constant pool for the type; (7) fieldinformation; (8) method information; (9) all class variables declared inthe type except constants; (10) a reference to class CLASSLOADER; and(11) a reference to class CLASS. Each of these kinds of information iswell known to those in the art who design Java virtual machines andprogram in Java.

Referring to FIG. 3, whenever an object 38 is created by a Javaapplication, memory for the new object 38 is stored in the heap 26.Because there is only one heap 26 inside of any instance of a Java VM10, all threads share the heap 26 and because each Java application runsinside its own Java VM 10, there is a separate heap 26 for every Javaapplication running. In this manner, one Java application cannot affectthe objects 38 in the heap 26 of another application. Two differentthreads 40 and 42 of the same application, however, could affect eachother's heap data, i.e. the objects 38. For this reason, synchronizationof the access to objects of multiple threads must be planned.

The existing Java VM 10, as illustrated in FIGS. 1-3 has severaldisadvantages. First, it is inherently redundant. Referring to FIGS. 4Aand 4B, a single computer when running multiple Java applications (orother applications that run in a VM) typically create a separate VM foreach application. Each VM, in turn, generates its own method area, heap,PC register, etc., using a good deal of the resources of the underlyingcomputer. This is true even when each VM is running a separate instanceof the same application where many of the objects created by theapplication will be identical. This is illustrated in FIG. 4B wherethree computers 46, 48, and 50 are running the same application 54through a server 52. In this instance, many of the runtime data areasmay be located on the server 52, creating the same kind of redundancy asseen in FIG. 4A.

The redundancy of existing VM systems translates to a loss in systemspeed for two reasons. First, each VM must use its own resources, i.e.time, to load objects already loaded in other applications. Second, thecombined memory space of all VM applications often bottlenecks systemresources. In many cases, the speed at which an application or series ofsimultaneously running applications may operate defines the upper limitof a system's performance—the number of trades processed, web pagesserved, or billing records updated per second. In other words, the speedat which individually well-tuned processes can operate determines howmuch value that system can provide on a second-to second basis, i.e.lost system speed means lost revenue.

The existing wisdom is that the redundancy and the associated loss ofspeed that results from designing every VM application to run in its ownisolated VM 10 is a small price in exchange for the assurance that oneapplication cannot change or otherwise corrupt the data being used byanother application. In addition, the isolation of applications eachwithin its separate VM ensures that if one application should close, orsuddenly crash, the other applications would remain unaffected. Thepresent inventors, though, came to the realization that there are avariety of applications in which the sharing of data across applicationsmight actually be beneficial. In those instances, the redundancy of theexisting system for running VM applications and the associated loss ofsystem speed would be needless.

With this in mind, FIG. 5 shows an improved system for running VMapplications, which broadly stated may comprise a shared object space100 and a native access layer 102 operably connectable with a pluralityof application programming interfaces (API) 104, 106 of independent VMsor other applications such as the C/C++ application 112. The accesslayer 102 permits each application 112, 114, through its associated, API104, 106 to load objects 108 into the shared object space 100 where theobjects 108 may be read and/or modified by the particular applications112, 114. Although in some instances, the individual applications mayduplicate some of the objects 108 stored in the shared object space 100within its own respective heap or other memory area, the shared objectspace 100 permits an application to store an object 108 in the sharedobject space 100 instead of its own heap or other memory area, thusavoiding the redundancy of existing VM systems. Access to the objects108 in the shared object space 100 may be synchronized for controllingaccess to shared objects in a heap by multiple concurrently runningthreads. Further, the shared object space 100 will store an object 108so long as a thread of any connected application is using the object108. In this manner, even if the application that placed a particularobject in the shared object space 100 closes or crashes, that objectwill still be available to other applications as necessary. Thus theshared object space 100 permits multiple applications runningsimultaneously on a system or network to enjoy the stability of existingVM systems, while providing a substantial boost in performance.

The shared object space 100 is accessible to an application through thenative access layer 102. Thus a Java application or other objectoriented application will recognize the shared object space 100 assimply another resource accessible through the native methods interfacethat already exists in Java and other object-oriented applications. Onceaccessed, all the functionality of the shared object space 100 will beinstantly accessible to the connected application. Further, the sharedobject space 100 does not need to be tied to a particular VM, butinstead is backwards compatible with any individual VM, whether it is astandard Java VM provided by Sun Microsystems or a customized VM of aparticular business, and forwardly compatible with any VM includingimprovements that have yet to be developed. Thus the versatility of theshared object space 100 can not be overstated. The versatility of theshared object space 100 is furthered by its compatibility with a widevariety of application interfaces. As can be seen in FIG. 5, the nativeaccess layer 102 provides access to the shared object space 100 by bothJava applications and C or C++ applications. It should be understoodthat these examples are illustrative only, and that the native accesslayer 102 could provide access to the shared object space 100 by anumber of other application types, whether object-oriented like Java orcommand oriented like C or C++.

The advantages of the shared object space 100 are readily apparent,particularly with respect to applications that benefit from the abilityof multiple, simultaneously running applications to update a sharedobject rather than simply read or copy a shared object. One suchapplication might be online trading. As the popularity of online tradingincreases, trading exchanges are faced with ever-growing volumes ofmarket data and concurrent trader activity. Systems that were built tohandle moderate volumes now have to handle thousands of traders andbillions of dollars in daily transactions. Such systems have toaccommodate huge spikes in demand. For instance, a single trade mayrequire thousands of traders to be notified. Many traders watch forthese price changes, then jump in to sell or buy very quickly, causingeven more notification demand and more trading volume. The faster atrading system reacts to changes, the more transactions an exchange canexecute, increasing its commissions while maximizing trader satisfactionwith the service.

Another example of the utility of the shared object space 100 might beits potential in improving speed of computerized activity in thetelecommunications industry. Modern telecommunication networks have toprocess vast amounts of data very quickly. Every time a call is placed,for example, an application needs to access the customer's subscriptioninformation, apply any special discounts that may be applicable, monitorthe call duration and establish a rate based on the time and distance tothe terminating number. Given that the number of such calls can run intothe thousands at any given moment, a memory based data sharing facilityis a necessity. In the past, such telecommunications applications havebeen written from scratch in C at enormous expense. The availability ofan off-the-shelf shared memory component that provides a shared objectspace 100 makes it possible to write such systems in Java or anotherobject-oriented program more quickly, cheaply, and with less risk.

Yet another example of the utility of the shared object space 100 is itspotential use in large scale internet applications. Large internetcontent syndication and portal applications depend on fast caching forscalability. The shared object space 100 provides an ideal cachingfacility for HTML and XML fragments, XML DOMs and streams, HTTP sessioninformation, and JDBC query results. It can also hold very fast pagerequest queues and other operational data structures. The shared objectspace 100 may include multi-language support which may be exploited whenconnected to web servers, servlet engines, content management suites,and XML transcoders to speed up every phase of a sites operation.

In use, the shared object space 100 may be one element in a largercomputing system 101. Specifically, it is anticipated that the sharedobject space 100, along with its associated native access layer 102 maybe used in conjunction with a console 118, an administrative processor120, disk storage 122 and a display 124 suitable for displaying systemstatistics. The console 118 is used to configure and start the system101 which may comprise a system manager 126, the shared object space100, and the native access layer 102. The system manager 126 creates andinitializes the shared object space 100, collects garbage, gathersstatistics, and logs both system and user-defined events. Once thesystem 101 has been started, the system manager 126 can also be used tobrowse the shared object space 100, enable statistics collection fromindividual objects, and display the statistics graphically for analysis.

The system 101 is preferably stored on a disk 122 in a defaultdirectory, e.g. “defaultSystem”, that holds the system's configurationfile and log file. The system 101 may be included on an executablestorage media such as a compact disk that include an installation toolthat may be used to create the requisite directories on the disk 122.Additional custom system directories may also be installed on the samedisk 122 as desired. Preferably, the system 101 includes a number ofdefault tools that operate on the default system; however the console118 and a command line utility may allow the user to specify a differentsystem.

To make use of the system 101 and its shared object space 100, thesystem 101 includes a library file in the default directory. Javaapplications should include a reference to this library (e.g.productdir/lib/gemfire.jar) on its CLASSPATH. On Windows systems, thelibrary may be made available by adding productDir/bin to PATH and onSolaris, the library can be made available by adding productDir/lib toLD_LIBRARY_PATH. An application process connects to the system 101 bymaking a call that contacts the system manager 126, such asGemFireConnection.myConn=GemFireConnection.getinstance (“Gemfire”). Thesystem manager 126 then returns information that enables the applicationprocess to map the shared object space 100 into its address space.

Each system 101 preferably maintains a global name space 116 in theshared object space 100. The name space 116 provides a fast objectregistry in which applications can register and look up “root” objectsby name. Objects that are referenced from this name space are protectedfrom garbage collection. Once connected to the system 101, anapplication can look up shared objects in the name space 116 with acommand such as Stock myStock = (Stock) myConn.lookup(“GSI”)A shared object like myStock always represents a current shared value;that is all threads in all VMs always see the same field values, just asall threads in a single VM see the same volatile field values for anobject in that VM. The statement

-   -   myStock.getPrice( )        for example, might return the price most recently set by a local        or remote thread, while the statement    -   myStock.setPrice(34)        immediately updates the shared view of myStock's price. Because        these fetches and updates incur no disk or network overhead,        they are much faster than the same operations implemented        through mechanisms like RMI and they outperform JDBC calls by an        even wider margin.

The system 101 may include a Class Enhance tool that prepares anapplication class for sharing by modifying the class's bytecodes toprovide transparent instantiation in shared memory and automaticread-through and write-through for field access methods. By default, allfields may be shared, but a user may establish more selective policiesby providing an XML description of the fields to be shared in eachdomain class. Once a class is enhanced, making an object of that classautomatically puts the object into shared memory.

Referring to FIGS. 6 and 7, the system 101 may support two methods ofsharing objects, copy sharing and direct sharing. An object 128 that iscopy shared is allocated twice, once in the local memory of anapplication and again in shared memory 100. FIG. 6 shows an example of acopy sharing method where application A creates an object 128 in itslocal address space. The object 128 is shared by putting it into theshared name space 116. At this point, the object 128 is not immediatelywritten to a field in the shared object space 100; instead the object128 is written to shared memory 100 only after a user “flushes”, i.e.updates the object to a new version, for the first time. Once an object128 is written to shared memory, application B is able to copy theobject 128 to its local memory by accessing the shared object 128 byname in the shared name space 116. Application B may modify the copy ofthe object 128 obtained from shared memory, and may also flush to updatethe shared memory copy of the object. If application B wishes to see themost recently updated version of the object 128, a refresh command maybe used.

FIG. 7 shows an example of a direct sharing method, which is a one-spacemodel where some of all of the non-static fields of the shared object128 reside only in shared memory. Static fields may be kept in the localheap of an application's VM for performance reasons. An assignment to afield of a directly shared object 128 is immediately visible to threadsof other applications and each application is able to write to theshared object. When the field is read, the current state in sharedmemory 100 is returned; there is no need to refresh the local memory.

FIG. 8 shows another system 201 that includes a shared object space 200within a first Java VM 202. The first Java VM 202 may include all theelements of a typical Java VM as previously described, i.e. a methodarea, a class loader, an execution engine, etc. The heap of the firstJava VM, however, acts as the shared object space 200 so as to beaccessible by the execution engine 204 of a second Java VM. In thesystem 201, the first instance of an application may initiate a VM whoseheap performs as a shared object space for subsequent instances ofapplications operating on the same computer. The shared object space 200may have all the functionality of the shared object space 100 previouslydescribed.

FIG. 9 shows another system 301 in which a shared object space 300resides on a server 302 interconnecting independent computers 304, 306,308 operating on the same or different platforms. Each computer 304,306, and 308 is running a VM instance of a single application that readsand/or writes to data in a database on the server 302. For example, theserver 302 may include a dynamic database for stock prices in a tradingscenario where the connected computers 304, 306, and 308 may be used tocomplete stock transactions through the server using a uniform softwarepackage.

As stated previously, when multiple threads from multiple applicationsare sharing objects in a shared object space, access to the objectsshould be synchronized. FIG. 10A illustrates this necessity. In thisfigure, application 302 is running in a VM 304 while application 306 isrunning in another VM 308. Both VM 304 and VM 308 are sharing the sharedobject space 300 that is storing a shared object 310. In this figure,application 302 is simultaneously running two threads, thread 312 andthread 314, both of which are calling shared object 310. At the sametime, application 308 is running a thread 316 which also is calling theshared object 310. Absent synchronization, each thread 312, 314, and 316could all access the shared object and make simultaneous, possiblyconflicting changes to the object 310 without any knowledge of eachother's changes.

Also, as stated previously, existing methods provide for synchronizationof multiple threads in a single application accessing a shared object ina single VM. Extended synchronization techniques, as described herein,may be used to provide synchronization for concurrent access to objectsin shared memory by multiple applications illustrated in FIG. 10B.

In FIG. 10B, a shared object space 300 stores objects O, P, Q, and R.Each of these objects includes an object header 320. Each object header320 may include a lock info field 322 which is used to indicate whethera thread of an application has locked that object. The lock info field322 may contain either a “cheap lock” or a reference to a “lock node”,i.e. an “expensive lock.” A “cheap lock” directly encodes the identityof the application and the thread that owns the lock by inserting avalue into the lock info field 322 unique to the thread of thatapplication. (The value “0” may be used to indicate that an object isnot locked by any thread of any application.) When thread A ofapplication 326 seeks to acquire object O, for example, thread A checksthe header of object O to test whether the value in the lock info field322 is “0”, representing that it is not locked. If the value is “0” thenthread A 324 substitutes its unique number in the header of object O andacquires the lock with a “cheap lock.”

This compare and swap informs subsequent threads that wish to acquireobject O that the object is “locked” and these threads will wait. Thiscompare and swap is preferably “atomic” in nature, meaning that theissued command(s) is performed in such a manner that there is nopotential for another thread to lock the object in the interim,especially when the command is executed by the processor. In many cases,the swap is performed in a manner internal to the microprocessor, and isaccordingly a very efficient mechanism. For example, if thread B 328seeks to acquire the object O while thread A 324 already has it, threadB will test to see whether the lock info field 322 is “0”. The test willfail and thread B will recognize that thread A has the object because ofthe number in the header. At this point, thread B does several things.Thread B makes two entries in a lock table 332 called “lock nodes” 336and 337. Also, thread B updates the “cheap lock” of the lock info field322 to an “expensive lock” that contains a reference to the lock node336 in the lock table 332. Thread B then goes to sleep waiting on itslock node 336. When thread A is finished it notifies the lock manager334 which removes the lock node 336 from the lock table and swap's B's“expensive lock”. i.e. a reference to the lock node 337, into the lockinfo field 322 of the object's header. Thread B thereby gains control ofthe object.

A lock node, such as 336 and 337, is an internal object, not visible tothe application. When a lock node is created, it is added to the locktable 332. If a thread of an application wanting to acquire the lockmust wait for another thread to release the lock, it waits on the uniquelock node object representing its lock request. The lock table 332 holdsinstances of lock nodes. A given lock node in the table representseither a thread that currently holds a lock or a thread that is waitingto acquire a lock. The lock node contains information pertaining to thevirtual machine that has or wants the object, as applicable, the threadthat has or wants the object, as applicable, and the object had orwanted, as applicable. When the lock manager 334 successfully grants alock to a thread by setting the target object's lock info field 322 tobe a reference to the lock node representing the waiting thread, usingthe compare and swap technique, it signals the lock node. The waitingthread then gets the object and proceeds.

All of the aforementioned activities of thread B occur without anyeffect on thread A. Stated differently, thread A is unaware of anythingthat B is doing and hence is not slowed down by thread B's activities.When thread A is finished and seeks to release the lock on object O, itwill check the lock node 336 and see that there are one or more threadswaiting for access to the object O. A first assumes that the lock isstill a “cheap lock” and does a compare and swap. If the lock has beenupdated to an expensive lock, its value is no longer in the lock infofield, so the test and swap will fail. In that case, two implementationsmight occur.

In the first implementation, the object's lock info field is set to “0”and the lock manager is signaled that there may be another lock node inthe lock table that can be granted the lock. (This is generally fasterfor the application thread). The lock manager 334 will then consult thelock table to see which thread has priority, in this case thread B, andtherefore grant thread B access to object O, at which point thread B's“expensive lock” will be inserted in the header of object O, etc. Thesecond implementation is that the thread, i.e. A, does the work ofdetermining the next owner of the lock and atomically changes theobject's lock info field 322 from a reference to its lock node to areferenced to the next owner's lock node. This eliminates the need for alock manager, at the expense of making the application slower.

The following is an example of a Java program fragment that might beused to invoke the procedures described above: Lockservice.synchronize ( anObject,new Runnable ( ) {   Lockservice.notify (anObject);  Lockservice.wait (anobject);  } );

The following is an example of a C fragment that may be used to invokethe procedures described above: Status = gfacquireLock(employee) doWorkgfReleaseLock(employee)

The foregoing examples illustrate the process that would occur if twothreads were contending for access to the same object. The foregoingexamples also illustrate the language neutrality and interoperability ofthe disclosed system. Obviously there may be quite a few threads seekingaccess to an object simultaneously, and in that event the foregoingprocedure will control the priority of access in an orderly fashionthrough the lock table 332 which records the relative priority of accessto an object between multiple threads. In the foregoing example, accessto an object by multiple threads is granted in order of the requests,i.e. first come, first served. Other systems may be used. For example,some systems may provide for threads to be indicated as priority threadswhose function is of some critical importance, and their place in thelock table accordingly bumped up. In some cases there is no guarantee topriority of access, so that if threads B. C. and D all try to obtain alock while thread A has it, thread B may not be next in line even if itwere the first to try to obtain the lock with respect to threads C andD.

The advantage of the foregoing system is a considerable boost in speed.For example, when there is no contention for an object at the time athread is trying to acquire it, the object may be obtained by a threadin as little as 10 microseconds. Where there is contention, however, itmay take more than 100 microseconds to acquire the object after it hasbeen released. Thus the ability to quickly detect whether or not thereis contention for an object permits a thread to acquire the object bythe quicker method.

FIG. 10B shows that object O is the parent of objects P and R and objectP is the parent of object Q. Objects O, P, Q, and R each have headerswith a lock info field 332. Therefore, threads are able to obtain objectQ, for example, without needing to lock any of the other objects,freeing them for use by other threads.

The terms and expressions that have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only the claims that follow.

1. A system for the concurrent operation of plural computerapplications, said system comprising: (a) a shared object space capableof simultaneous connection with plural said applications and capable ofstoring at least one object accessible to at least two said applicationswhen said plural applications are connected with said shared objectspace; (b) a lock table for storing lock nodes, each said lock nodebeing uniquely associated with a one of said plurality of applications;(c) said at least one object having an object header capable of storingany selective one of: (1) a selective said lock node; (2) a reference toa selective one of said lock nodes stored in said lock table; and (3) adefault value other than one of said lock nodes or a reference to one ofsaid lock nodes stored in said lock table.
 2. The system of claim 1where said default value is zero.
 3. The system of claim 1 where saidlock table is located in said shared object space.
 4. The system ofclaim 1 where said selective one of said lock nodes operates as a cheaplock when stored in said object header.
 5. The system of claim 4 wheresaid reference to a selective one of said lock nodes stored in said locktable operate as an expensive lock when stored in said object header. 6.The system of claim 1 where said reference to a selective one of saidlock nodes stored in said lock table operates as an expensive lock whenstored in said object header.
 7. The system of claim 6 where a saidapplication that has a said expensive lock to a said at least one objectgrants said lock to another said application by swapping one of saidselective one of said lock nodes, said reference, and said default valuefor another one of said selective one of said lock nodes, saidreference, and said default value.
 8. The system of claim 1 including alock manager that controls access to at least one object by selectivelyswapping one of said selective one of said lock nodes, said reference,and said default value for another one of said selective one of saidlock nodes, said reference, and said default value.
 9. The system ofclaim 8 where said swap is atomic.
 10. The system of claim 1 where saidat least one object comprises a plurality of sub-objects, each saidsub-object having a said object header.
 11. The system of claim 1 whereeach said plural application runs in its own virtual machine.
 12. Thesystem of claim 11 where each said virtual machine is a Java virtualmachine.
 13. The system of claim 12 where said shared object space isconnected to each said Java virtual machine by a Java native methodinterface.
 14. The system of claim 1 where at least one of said pluralapplications is not an object oriented application.
 15. The system ofclaim 14 where said at least one of said plural applications is a Capplication.
 16. A method for synchronizing access to a shared objectstored in a shared object space by plural computer applications, saidmethod comprising: (a) storing at least one object in a shared objectspace so that said object is accessible to at least two of said pluralapplications when said plural applications are connected to said sharedobject space, said at least one object having an object header; (b)selectively storing at least one lock node in a lock table, each saidlock node being uniquely associated with a one of said plurality ofapplications; and (c) storing in said object header any selective oneof: (1) a selective said lock node; (2) a reference to a selective oneof said lock node stored in said lock table; and (3) a default valueother than one of said lock nodes or a reference to one of said locknodes stored in said lock table.
 17. The system of claim 16 where saiddefault value is zero.
 18. The system of claim 16 where said lock tableis located in said shared object space.
 19. The system of claim 16 wheresaid selective one of said lock nodes operates as a cheap lock whenstored in said object header.
 20. The system of claim 19 where saidreference to a selective one of said lock nodes stored in said locktable operate as an expensive lock when stored in said object header.21. The system of claim 16 where said reference to a selective one ofsaid lock nodes stored in said lock table operates as an expensive lockwhen stored in said object header.
 22. The system of claim 21 where asaid application that has a said expensive lock to a said at least oneobject grants said lock to another said application by swapping one ofsaid selective one of said lock nodes, said reference, and said defaultvalue for another one of said selective one of said lock nodes, saidreference, and said default value.
 23. The system of claim 16 includinga lock manager that controls access to at least one object byselectively swapping one of said selective one of said lock nodes, saidreference, and said default value for another one of said selective oneof said lock nodes, said reference, and said default value.
 24. Thesystem of claim 23 where said swap is atomic.
 25. The system of claim 16where said at least one object comprises a plurality of sub-objects,each said sub-object having a said object header.
 26. The system ofclaim 16 where each said plural application runs in its own virtualmachine.
 27. The system of claim 26 where each said virtual machine is aJava virtual machine.
 28. The system of claim 27 where said sharedobject space is connected to each said Java virtual machine by a Javanative method interface.
 29. The system of claim 16 where at least oneof said plural applications is not an object oriented application. 30.The system of claim 29 where said at least one of said pluralapplications is a C application.
 31. A system for the concurrentoperation of plural computer applications, said system comprising: (a) ashared object space capable of simultaneous connection with plural saidapplications and capable of storing at least one object accessible to atleast two said applications when said plural applications are connectedwith said shared object space; (b) said at least one object having aheader capable of storing a lock that indicates that one of said pluralapplications is using the object associated with said header; and (c)said lock being either a cheap lock or an expensive lock, said cheaplock defined as a lock that may be inserted into or removed from saidheader in a relatively short time with respect to said expensive lock.32. The system of claim 31 where said header stores an expensive lockwhen one said application is waiting for said object associated withsaid header while another said application is using said objectassociated with said header, and said lock is a cheap lock otherwise.33. The system of claim 31 including a lock table capable of storing aplurality of lock nodes, each said lock node being uniquely associatedwith a one of said plurality of applications.
 34. The system of claim 33where each said application is capable of using said at least one objectthrough a plurality of threads and said lock table stores information asto which threads are waiting for an object being used.
 35. The system ofclaim 34 where said threads waiting for said object being used areprioritized to determine which of said threads next gets access to saidobject being used.
 36. The system of claim 34 where said threads waitingfor said object being used are not prioritized to determine which ofsaid threads next gets access to said object being used.
 37. The systemof claim 31 where said header contains a default value when said headerdoes not contain a lock.
 38. The system of claim 37 where said defaultvalue is zero.
 39. The system of claim 33 where said lock table islocated in said shared object space.
 40. The system of claim 33 where asaid application that has a said expensive lock to a said at least oneobject grants said lock to another said application.
 41. The system ofclaim 33 including a lock manager that controls access to at least oneobject.
 42. The system of claim 31 where said at least one objectcomprises a plurality of sub-objects, each said sub-object having a saidobject header.
 43. The system of claim 31 where each said pluralapplication runs in its own virtual machine.
 44. The system of claim 43where each said virtual machine is a Java virtual machine.
 45. Thesystem of claim 44 where said shared object space is connected to eachsaid Java virtual machine by a Java native method interface.
 46. Thesystem of claim 31 where at least one of said plural applications is notan object oriented application.
 47. The system of claim 46 where said atleast one of said one said plural applications is a C application.